Rubber antioxidants



ms 5. 15, 1042 I 2,295,985

2,295,985 animus. moxmams William Baird and Maldwrn Jones, Biackley, Manchester, England, assignors to Imperial I UNITED STAT-ES PATENT OFFICE I after exposure to light.

Chemical Industries Limited, a

. Great Britain corporation or No Application January 29, 1940, Serial vs Claims. (01. 200-619) According to this invention we manufacture vulcanlsed rubber by vulcanising rubber hot in a mixture comprising added sulphur, vulcanisation accelerator and an antioxidant oi the class defined below.

The said class consists of bis-(2-hydroxy-3z5- dimethylphenyl) alkylniethanes, in which the al- 4 kyi radical has not more than 6 carbon atoms.

By using this class c: antioxidants in the way described above, rubber vulcanisates are obtained, which have very good resistance to ordinary ageing and which, in the case of white or clear coloured vulcanisates, are little if at all stained,

British Patent No. 413,012 describes a cold vulcanisation process in which there is used as antioxidant a bis- (hydroxyphenyl) methane, which is substituted in at least 2 positions, one ortho to each hydroxyl group, which substituents are preterably methyl groups, and in which one or both or the methylene hydrogen atoms may be sub-- stituted, e. g. by the same or diilerentstraightchain hydrocarbon residues. The antioxidants oi the present invention conier greater to oxidation than do those of British Paten 413,012.

The antioxidants oi this invention are new compounds and may be made by condensing 2:4- dimethylphenyl with the appropriate aliphatic aldehyde in the presence of an acid condensing agent, e. g. hydrochloric or sulphuric acid.

The iollowing examples, in which parts are by I weight, illustrate but do not limit the invention.

Example 1 m Bis-(2-hydroxy-3z5-dimethylphenyl) ethane is included in the following rubber mix:

alter exposure to light is obtained.

No. 316,226. In Great Britain February 2'1,

a! a'. Bis -(2-hydroxy-3:5-dimethylphenyl) ethane may be made by boiling under a reflux condenser for 24 hours a solution of 40 parts of 2:4- dimethyiphenol. 10 parts of acetaldehyde and parts of hydrochloric acid in 120 parts of ethyl alcohol, cooling, filtering, drying and recrystallising from benzene. It melts at 132-5 C.

In place of the antioxidant used above, there may be employed, for example, aia-bis-(Z-hY- droxy-3z5-dimethylphenyl) butane, -isobutane or -heptane, which possess similar properties as antioxidants. These compounds may be prepared by the method described above for the corresponding ethane derivatives by using.n-butalde hyde 0r iso-butaldehyde (CHahCILCHO, or n- .heptaldehyde in place of acetaldehyde. They have melting points as shown below:

aid-B18 (2-hydroxy-3 5-dimethylphenyl) butane,

M. P. 123 C.-

aid Bis- (2-hydroxy-3 S-dimethylphenyl) isobutane, M. P. 158 -9 C.

aiw- Bis (2 hydroxy-3z5-dimethylphenyl) heptane. M. P. 133-5 0.

Example 2 To illustrate the greater resistance to oxida- 7 tion conferred by compounds of the invention compared with compounds previously mentioned as non-staining antioxidants and related-chemically tofthose oi the present invention, mixes containing the various antioxidants .were prepared as described in Example 1, vulcanised and subjected to tests. Accelerated ageing tests were done at C. in oxygen at 800 lb./sq. in. The

' resistance to ageing was determined by the loss in tensile strength, in the usual manner, the following results obtained:

Parts Pale crepe rubber; Zinc oxide 10 4o, igfigfi Blane nxe g x '15 Antioxidant 'rltanimn dioxide..-- 10 a Mm Btearic acid 1' 9$; 12 days Sulphur I as,

r a g figmg m 2' as as 2.-' hydroxydbdlm' ethylphenyi) j -1az 14s The as is then at 141 c. for 25 Bni-h ydm -tzfi-dim th 1 ethane" mo 01 vulcanisate with very good resistance fag'wzgyphwl) to ordinary ageing and substantially unstained m v stiezio'isnts in the above men onesi in British is on antioxidant of Gull Patent too;

These resuits siio e'iesri; the superiority oi? a: o: is -(?2iiys1rox3"-3 ii=dimethyiphenyn butane over the other antioxidants tested as regards re sistance to oxygen. on the staining efiect of exposure to ultrewioiet light were also made. These showed his-(Z-hydroso -3 :5-dimethy1phen= yDbutsne to be slightly superior to the known substances mentioned in this example. It is to be noted that ,3: ,8-bisi-hydroxy-B 5-dimethy1 phenybpropene retards cure markedly.

The compounds (12c: sis -(2-hydroxy-3;5-=dimethylphenyl) ethane, -isobutane and heptane are substantially equal to the -butane compound in antioxidant and non-staining properties, when tested under the conditions described in this example.

Example 3 Mixes were prepared as described in Example 1, vulcanised and the vulcsnisates subjected to accelerated ageing tests in an air oven at 70 C. for 6 weeks and tensile strength determinations The above test figures show that the butane,

isobutane end neptane derivatives confer a high degree of resistance to ageing in the air oven.

We claim:

1. Bis-( hydroxy-3: 5-dimethylpheny1) alkylmethane in which the alkyl radical has not more than 6 carbon atoms.

2. Bis- (2 hydroxy-ii: 5-dimethy1phenyl) n-propylmethane.

3.. Bis (2-hydroxy-3: 5-dimethylphenyl) isopi'o- V pylmethane.

WILLIAM BAIRD. MALDWYN JONES. 

